In open heart surgery, one technique for achieving a motionless heart prior to surgery includes the use of induced hypothermic cardioplegia. This involves the infusion of a cardioplegic solution into the coronary arteries at a low temperature. The chemical composition of the solution varies with different coronary operative teams but one chemical common to all cardioplegic solutions is potassium.
The heart contracts in its normal rhythmic pattern as a result of electrical impulses that are initiated in an area of nerve tissue called the sinoatrial node which is the natural pacemaker for the heart. Potassium in the cardioplegic solution causes an immediate arrest of electrical impulses to the heart. The heart also has a need for oxygen supplied to the heart muscle under normal circumstances The use of a low temperature solution begins to reduce the heart's oxygen consumption rate. The combination of the potassium and the cooling makes it possible for surgeons to perform heart surgery without damage to the heart.
Since it is desirable to arrest heart action for as short a time as possible, the procedures for introduction of the cardioplegic solution must be accomplished as rapidly as possible. The present invention is directed to the control of the supply of the cardioplegic solution to the heart in an efficient manner. The switch may be situated at the cardioplegia source (the heart lung machine or "pump") or at the patient in close proximity to the open chest during the operational procedure. If the device is at the pump, the perfusionist will perform the switching, whereas if it is at the patient, the operating surgeon controls the mechanism. The present disclosure is directed primarily to a unit for use by the operating surgeon. It is generally agreed that myocardial ischemia, that is, withholding the blood from the heart, should be maintained for as brief a period as possible.
The invention involves the use of a supply of cardioplegic fluid which can be applied to the heart at the coronary area in antegrade flow or in the venous area in retrograde flow. With the chest rib cage open, the aorta, which arches over the heart and normally supplies oxygenated blood to the body, is clamped above the heart and an antegrade cannula inserted into the aortic root and sutured. In addition, the coronary sinus is cannulated and a cannula secured for flow into the venous structures of the heart. Thus, there are fluid branches to the aorta and to the venous structures which is the venous side of the heart.
In the extracorporeal system for supplying cardioplegic fluid, a control switch is incorporated at the root of the two fluid branches and, by manually operating the switch, the fluid can be directed to the aorta branch or to the venous side of the heart. The switch has a prime position which allows access to both branches to prime the system. The switch, when moved to an antegrade or retrograde position, operates to close one branch and open the other. The switch is so designed that one branch is closed while the other is open or vice versa. In the switch, pressure monitoring lumens may be incorporated.
The main object then of the control switch is to permit the perfusionist or the surgeon to introduce cardioplegic fluid either to the arterial side of the heart or to the venous side of the heart. In antegrade perfusion if there are occlusions or partial occlusions on the arteries, the cooling may not reach all areas of the heart rapidly. Accordingly, switch to the venous side of the heart (retrograde) furnishes fluid to a large part of the heart and speeds the cardioplegic action. In practice, a portion of the cardioplegia dose can be directed antegrade and the balance of the dose can be directed retrograde.
In addition to the cardioplegic fluid, some heart surgeons utilize ice slush to cool the heart and, in some instances, insulate the far side of the heart from the body.
Additional features and objects of the invention will be apparent in the following description and claims in which details of the invention are set forth, all in connection with the best modes presently contemplated for the practice of the invention.